Efficacy of Calcium Hypochlorite on the Prevalence of Microsporidiosis (Thelohania) in Pond-Reared Litopenaeus vannamei

Abstract

The efficacy of calcium hypochlorite for controlling microsporidian (Thelohania or Agmasoma) infection by treating the water before stocking Pacific white shrimp, Litopenaeus vannamei, postlarvae (PL) was studied in intensively cultured ponds. Five ponds (of 4 rai each) were used as the treatment group in which calcium hypochlorite at a concentration of 18 mg/l was added into the ponds while all the aerators were operating. In the control group, no calcium hypochlorite was used. PL10 were stocked at a density of 80 PL/m2 and shrimp were fed with commercial pelleted feed throughout the 120-day culture period. Results showed that the prevalence of microsporidian (Thelohania, Agmasoma) infection of shrimp in the treatment group was significantly lower than that of the control group (P<0.05). At day 50, the average highest percentage of microsporidian infection in the treatment ponds was 5.40% compared with 25.16% in the control ponds. The infected shrimp gradually died off or were eaten by the healthy shrimp so that after harvesting only a few infected shrimp were found. In conclusion, in shrimp culture areas where microsporidian outbreaks previously occurred, calcium hypochlorite at the concentration of 18 mg/l should be used for water treatment before stocking the PL.